Not applicable.
1. Field of the Invention
The present invention relates generally to systems for loading out large volumes of dewatered biosolids for transport, reuse, and disposal, and more particularly to a gravity flow sludge load-out system for rapid and highly controlled automated loading out of biosolids into container trucks.
2 Discussion of Related Art
The treatment and disposal of large volumes of sewage sludge has been a problem for many years. Numerous methods have been devised to render biological sludge generally pathogen free and suitable for reuse as soil amendment and fertilizer; and numerous other methods have been devised to make unusable sludge easier to transport for disposal. However, regardless of its ultimate destiny, treated sludge is typically stored briefly at a sewage treatment facility and then loaded out into containers for transport either to sludge customers or to disposal sites. And in facilities with high wastewater throughput, the sludge must be loaded out quickly and efficiently to avoid the accumulation of a large sludge inventory.
Furthermore, in the case of large municipalities, it is not uncommon for fertilizer plant sludge customers to demand a supply of several hundred thousand pounds of sludge each day. The logistics and mechanics of providing such an ongoing supply demands, firstly, that the system loads sludge quickly, not only to meet the demand for supply, but also to minimize time wasted by trucking and other transportation concerns; and, secondly, the system must load out the sludge with a high degree of accuracy, because municipalities must accurately track charges for the supply and must further maintain certified records pertaining to the disposition of specific amounts of hazardous waste. For billing purposes alone, the tolerances must typically be within xc2x11%. However, providing this degree of accuracy while simultaneously providing high throughput has not been achieved by prior art known to the present time. The source of the problem lies in large fluctuations in sludge flow rates, due, in turn, to large fluctuations in sludge viscosity caused by batch variants in sludge dehydration and temperature, and varying material heights or head pressures in the loading hoppers.
Another challenge in designing a sludge load-out system that provides rapid and accurate loading out is to provide a system capable of measuring real-time load-out status. Such a system feature is not merely desirable but mandatory at facilities where truck scales will not or can not be provided to measure loading status. Moreover, it is desirable to provide a variable load-out orifice to permit fine control of the sludge flow so as to minimize splattering and sludge loss; however, with such an orifice, flow meters cannot provide an accurate measurement of real-time flow. Finally, a system including real time sludge flow monitoring has not been devised in those systems in which hoppers are refilled while dispensing their content.
Accordingly, it is an object of the present invention to provide an automatic sludge loadout system that loads-out large volumes of sludge quickly and accurately.
It is a further object of the present invention to provide a sludge load-out system that measures real-time load-out status while also providing simultaneous load-out and hopper refilling.
It is yet another object of the present invention to provide a sludge load-out system that includes hoppers having variable load-out gate orifices.
The gravity flow sludge load-out system of the present invention provides a means for rapidly and accurately loading-out large volumes of treated biosolids from a wastewater dewatering plant. The system comprises at least one hopper, each supported by a main structure having a plurality of vertical support members. Each hopper rests on dedicated load cells. Each hopper has at least one inlet at the top for the introduction of sludge from the dewatering facility. Each hopper further includes a powered metering gate at the bottom, each including power means on each side, support rollers to support the gate blade, position sensors to establish the position of the blade during the load-out process, and proximity/limit switches to confirm fully opened and closed gate positions. The power means are preferably hydraulic, pneumatic, or electric cylinders having pistons connected to the metering gate blade.
Immediately above the hoppers is a sludge distribution container having a motorized distribution screw and outlets above each hopper. Interposed between the sludge distribution container outlets and the hopper are hydraulically controlled slide gates. Dewatered solids are conveyed from the dewatering facility centrifuges to the sludge distribution container via a conveyor system or pumped via pipes.
Movement of the mechanical components of the gate system, i.e., the slide gates and the metering gates, is powered by a power system, preferably hydraulic or pneumatic. The hydraulic power unit comprises a pump, a fluid reservoir, and at least one accumulator. The power unit is operatively connected to the slide and metering gates by a series of hydraulic lines. A comparable pneumatic power unit comprises a pump and accumulator.
To monitor load-out status and control load-out function, the system includes a control panel comprising a programmable logic controller (PLC), connected to a personal computer, at least one operator interface stations, the load cells, and, optionally, a dewatering facility magnetic flow meter. The PLC is also coupled to valve panels for each slide gate and each metering gate to selectively position or stabilize the gate blade.